Polythioaminal dispersions and coatings

ABSTRACT

Methods of forming and using a polymer dispersion are described herein. The polymer dispersion includes a plurality of polythioaminal microparticles in a fluid medium that does not dissolve the plurality of polythioaminal microparticles. The fluid medium may be aqueous, for example water. The polymer dispersion may be applied to a substrate, and the fluid medium removed, to form an article substantially made of a polymerized polythioaminal mass. The dispersion, and any article made from the dispersion, may include pigments and active ingredients, such as biocides.

FIELD

The present invention relates to methods of making liquid dispersions ofpolythioaminal particles, and coatings made from such dispersions.

BACKGROUND

A latex is a stable dispersion of polymer microparticles in a liquidmedium, which is usually an aqueous medium. Various polymers areconventionally applied via a latex to form a coating or an adhesivelayer. The polymer is dispersed in the liquid medium, stabilizers suchas surfactants are added to stabilize the dispersion. If a coating isdesired, the mixture is applied to an article to be coated, and theliquid is evaporated to leave a polymer coating. If an adhesive isdesired, the mixture is applied to one article to be adhered to form anadhesive layer, a second article to be adhered is contacted with theadhesive layer, and the articles are held in place while the adhesivedries. Most polymers used in this way are rubbers such as naturalrubber, but a latex may generally be used to perform emulsionpolymerization of, for example styrene to make polystyrene or styreneand butadiene to make synthetic rubber. Polymers applied in this fashiontypically have limited uses. There is a need to broaden theapplicability of latex methods to polymers having more uses.

SUMMARY

Methods of forming and using a polymer dispersion are described herein.The polymer dispersion includes a plurality of polythioaminalmicroparticles in a fluid medium that does not dissolve the plurality ofpolythioaminal microparticles. The fluid medium may be aqueous, forexample water. The polymer dispersion may be applied to a substrate, andthe fluid medium removed, to form an article substantially made of apolymerized polythioaminal mass. The dispersion, and any article madefrom the dispersion, may include pigments and active ingredients, suchas biocides.

DETAILED DESCRIPTION

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Similarly, the terms “furthercomprises,” “may further comprise,” and “further comprising,” when usedin this specification, specify the presence of additional features orcomponents, without precluding the presence or addition of otherfeatures or components. The terms “further comprises,” “may furthercomprise”, and “further comprising” in this specification do not meanthat any features or components are excluded from any embodiments. Whena range is used to express a possible value using two numerical limits aand b (e.g., a concentration of a ppm to b ppm), unless otherwise statedthe value can be a, b, or any number between a and b.

The description of the present invention has been presented for purposesof illustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiments were chosen and described in order to best explain theprinciples of the invention and their practical application, and toenable others of ordinary skill in the art to understand the invention.

Polythioaminal polymers may be used to form articles by dispersing aplurality of polythioaminal microparticles in a fluid medium that doesnot dissolve the plurality of polythioaminal microparticles, applyingthe dispersion to a substrate, and removing the fluid medium to form asolid article. The solid article thus formed comprises a solid masscomprising a polythioaminal polymer.

Polythioaminal (PTA) polymers are polymers having a C—N—C—S—R—Srepeating unit or an S—R—S—C—N—R′—N—C repeating unit, where R is anorganic or hetero-organic group. The polymers are generallythiol-terminated, so a typical PTA molecule may have either of twogeneral structures:

Structure (1) is formed by reacting a substituted hexahydrotriazinesmall molecule with a dithiol, as follows:

The byproduct amine must be removed from the reaction to drive growth inmolecular weight of the PTA. This can be done by volatilizing the amineup to a temperature not more than about 200° C., or if the amine is notvolatile at such temperatures, by including an amine scavenger, such asa cyclic carbonate or anhydride, in the reaction mixture. It is helpfulin some embodiments for the amine scavenger to be orthogonal to theother reaction species (hexahydrotriazines and thiols). Propylenecarbonate and succinic anhydride are two useful examples of aminescavengers that may be used.

Structure (2) is formed by reacting a primary diamine and a primarydithiol together in the presence of paraformaldehyde, as follows:

In reaction [2], R³ is an organic or hetero-organic group that iselectron deficient. Thus, R³ may include aryl groups, CF₃, NO₂, and thelike. The electron-withdrawing activity of the R³ group forms a stableimine intermediate <C═N—R³—N═C> with paraformaldehyde that then reactswith the dithiol to form the PTA. R¹, R², and R³ can be functionaland/or oligomeric/polymeric to impart useful additional properties tothe PTA.

Reactions [1] and [2] above may be performed in solvent, or using theprecursors as solvent. Polar aprotic solvents such asN-methylpyrrolidone are useful for performing reactions [1] and [2]above. The reactions are typically performed under slight heating, forexample at 50° C. to 80° C., and growth of molecular weight thickens thereaction mixture. The polymer may be recovered by volatilizing residualsolvent and monomer, usually under vacuum to avoid approachingdegradation temperatures of the polymer. Upon recovery, the polymer maybe reduced to a powder of microparticles either by direct precipitationor by mechanical processing.

PTA microparticles recovered by a process as described above can be usedto form articles and coatings using a latex-style process. A pluralityof PTA microparticles are dispersed in a fluid medium that does notdissolve the plurality of PTA microparticles. The PTA material may beweakly soluble in the fluid medium, so some particles may dissolve toform a very low concentration solution in the fluid medium, but themajority of the particles remain suspended in the fluid medium. In somecases the fluid medium may be aqueous. In some cases the fluid mediummay be water. The PTA microparticle suspension is generally applied to asubstrate, which may be a surface or a mold, and the fluid medium isremoved. As the fluid medium evaporates, the PTA microparticles undergoemulsion polymerization to form covalent bonds between themicroparticles such that a solid mass, which may be a coating or solidarticle, is formed. The solid mass mostly consists of PTA moleculescrosslinked together in a polymer network.

Suspension of the PTA microparticles in the fluid medium may be aided byuse of solvents and surfactants to manage electrostatic interactionbetween the PTA microparticles and the fluid molecules. For example,hydrophobic PTA materials, such as mainly hydrocarbon-based PTAmaterials, may be dispersed in water using an ionic surfactant such assodium dodecyl sulfate to form micelles. In other embodiments, the PTAmay be fully dissolved in a good solvent, and then a poor solvent may beadded up to the cloud point of the mixture. Thus, in one embodiment, oneof the reactions [1] and [2] may be performed in a solvent up to adesired molecular weight, and then a second fluid that is a poor solventmay be added to form PTA micelles.

A second approach to generating microparticles uses cross-linking. Amulti-functional thiol precursor of the form R⁴(SH)_(n), where n isthree or more, may be added to dithiol and diamine or triazineprecursors in a dilute solution. Such a multi-functional thiolcross-linker may be used with either reaction [1] or [2] above toprovide cross-links between polymer chains, as follows:

The cross-linked polymer product has the following structures:

where R⁴ in this case is trivalent, but could have valence effectivelyup to 6. R⁴ may be an organic or hetero-organic group capable ofaccepting multiple thiol functionalizations. Note that individualpolymer molecules may have end groups formed from the dithiol, shown instructure (3B), or from the multi-thiol, shown in structure (3A). Ineach case, some repeating units are formed from the trithiol species,providing cross-links to other polymer chains, as denoted by wavy bondsto the sulfur atoms.

The polymer of structures (3A) and (3B) may be precipitated fromsolution by mixing with a miscible material that is a poor solvent forthe polymer molecules. In some cases, water may precipitate the polymer.The powder thus obtained, consisting of cross-linked polymermicroparticles may be dispersed in a fluid medium and applied to asubstrate to form an article of applied microparticles. If thecross-linked particles do not form micelles, the PTA dispersion may bedried to form a microparticle article, and then heated to form a solidarticle. The applied microparticles may be heated to a temperature of50° C. to 150° C. to form a uniform, continuously polymerized, solidarticle, which may be a coating.

The suspended PTA microparticles are applied to a substrate, asdescribed above, and dried to form an article. If the microparticles donot form micelles, as may be the case with particles of cross-linkedpolymer, the PTA dispersion may be dried to form a microparticlearticle, and then heated to form a solid article. In the cross-linkedcase, the applied microparticles may be heated to a temperature of 50°C. to 150° C. to form a uniform, continuously polymerized, solidarticle. The article may be a coating or a three-dimensional moldedarticle. Other ingredients may be added to the PTA suspension forvarious desired effects. The additives may be dispersed in the fluidmedium before or after dispersing the PTA microparticles. For example,in one embodiment a PTA suspension may be formed as follows: 1) add asurfactant to a fluid medium; 2) disperse PTA microparticles in thefluid medium; 3) disperse additives in the fluid medium. In anotherembodiment a PTA suspension may be formed as follows: 1) add asurfactant to a fluid medium; 2) disperse additives in the fluid medium;3) disperse PTA microparticles in the fluid medium.

The additives may include pigments, texturizing materials, visual effectmaterials, active ingredients, physical property modifiers, and otherpolymers. The active ingredients may include reactive species, flameretardant species, magnetic species, electrically conductive species,and bioactive species. Texturizing materials may include mineral orvegetal material such as mica, silica, bitumen, or cellulose. Flameretardant species may include phosphates, gypsum, perlite, and the like.Magnetic species may include iron particles and rare earth powders.Bioactive species may include fungicides, algicides, and bactericidessuch as hydantoins and isothiazolinones. Visual effect materials mayinclude light-emitting materials such as phosphors andelectroluminescent materials.

The additives may include components miscible with the fluid medium.Such additives may incorporate into the PTA article as the fluid mediumis evaporated. Some such additives may be reactive with the PTA medium.For example, thiol-reactive or amine-reactive materials may be includedin the fluid medium to react with residual thiol and amine sites in thePTA polymer that forms as the mixture dries. Thiol-terminated moleculesmay react with residual reactive thiol or amine sites of the PTA to addfunctionality to the article. Epoxide molecules may react with residualreactive amine sites in the PTA. If such molecules are difunctional,branching and cross-linking may be performed. For example, a di-epoxidemay be included with the PTA to activate a cross-linking reactionbetween the amine sites of adjacent PTA chains.

The additives may also be non-reactive, and may remain in the PTAarticle after the fluid medium is removed by simple coalescence. In somecases, intermolecular electrostatic forces may intermediate the affinityof additives for the PTA polymer. The additives may be functionalized insome cases, for example by adding or including electron-rich groups inthe molecular structure of the additive to provide an affinity forresidual amine or thiol protons of the PTA.

In such embodiments, it will be most useful if the thiol- oramine-reactive additives are less volatile than the fluid medium. Insome embodiments, a desired functionality may be provided in a moleculehaving molecular weight selected to limit volatility of the additive.For example, a low molecular weight polymer or oligomer may befunctionalized with the desired functionality and then dissolved in thefluid medium with the suspended PTA particles. As the fluid mediumevaporates, the PTA chains react to form the solid article, and thefunctionalized additive molecules remain in the PTA matrix eitherinterpenetrating with the PTA matrix or bonded to the PTA matrix in someway (e.g. covalently, ionically, or by Van der Walls electrostaticattachment such as hydrogen bonds).

In some embodiments, a coating or article may be made by a latexprocess, as described herein, including more than one application anddrying cycle. In a coating process, a first PTA/fluid medium mixture maybe applied to a substrate and dried to form a first coating, and then asecond PTA/fluid medium mixture may be applied to the substrate anddried to form a second coating. The second PTA/fluid medium mixture mayoverlap partially or completely with the first coating to form regionsof a layered coating. In such embodiments, the first and second coatingsmay be the same material, or different materials, and the first andsecond coatings may co-adhere through chemical bonding, for example bycovalent bonding of PTA molecules from the second coating with PTAmolecules from the first coating, or through interfacial processes suchas solution welding, in which PTA particles of the second PTA/fluidmedium mixture interpenetrate with the PTA matrix of the first coating.Either the first or second coatings may contain additives that promotedevelopment of a desired interface between the coatings. For example, anadhesive such as polyisobutylene, polyisoprene, or polycyclopentadienemay be dissolved or suspended in the second PTA/fluid mixture medium topromote adhesion. Alternately, an adhesive layer may be appliedcovering, at least in part, the first coating prior to applying thesecond coating.

Any number of such coatings may be applied to achieve a desired result.Each coating may be the same material as the previous coating, or adifferent material. For example, the first coating may be a PTA-basedmaterial that includes a PTA of structure (1) above and the secondcoating may be a PTA-base material that includes the same, or adifferent, PTA of structure (1) above. Likewise, the first coating maybe a PTA-based material including a PTA of structure (1) above, whilethe second coating is a PTA-based material including a PTA of structure(2) above. The first coating may include a second polymer, while thesecond coating includes no second polymer, or the second coatingincludes a second polymer different from the second polymer of the firstcoating. Either the first coating or the second coating, or both, or anysubsequent coating, may be applied according to a desired pattern sothat portions of the first coating may be exposed through the secondcoating to any desired degree.

The first coating and the second coating may be selected to providedesired processing characteristics. For example, the first coating mayhave a first susceptibility and the second coating may have a secondsusceptibility. If the first coating is blanket-deposited, and thesecond coating is pattern-deposited to expose portions of the firstcoating, a process may then be performed to selectively process thefirst or second coating depending on the different susceptibilities ofthe two coatings. For example, if the first coating includes a PTA ofstructure (1) above, and the second coating includes a PTA of structure(2) above, the substrate may subsequently be treated to apply an epoxidematerial to react selectively with the residual reactive amine sites ofthe PTA in the second coating while having no effect on the firstcoating. In this, way coatings can be combined and patterned to producearticles having a great diversity of surface features.

In some embodiments, an article made be molded using a latex process, asdescribed above, and then coating using a similar latex process with asimilar PTA-based material or a different PTA-based material. Theembodiments described above with respect to two or more coatings mayalso apply when an article is molded and then coated. A first PTA/fluidmedium mixture is introduced into a mold and allowed to dry andpolymerize. The article thus formed is unmolded and treated in anydesired way, for example shaped or textured, and then a second PTA/fluidmedium mixture is applied to the article and allowed to dry andpolymerize. The PTA microparticles in the second PTA/fluid mediummixture react with PTA molecules in the surface of the article, formingcovalent bonds between the coating material and the coated article.

Articles made according to the latex type processes described above maybe repaired by applying heat. PTA polymers undergo exchange reactionswhen heated. A damaged area of a PTA article, such as a coating, may beheated to activate an exchange reaction where PTA polymer chains growtogether to repair the damaged area. Localized heating to 100° C. orhigher is usually sufficient to activate the exchange reaction.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A polymer dispersion, comprising: a plurality ofpoly(thioaminal) microparticles; and a fluid medium that does notdissolve the plurality of poly(thioaminal) microparticles.
 2. Thepolymer dispersion of claim 1, wherein the fluid medium is aqueous. 3.The polymer dispersion of claim 1, further comprising a surfactant. 4.The polymer dispersion of claim 1, further comprising a pigment.
 5. Thepolymer dispersion of claim 1, further comprising a surfactant and apigment, wherein the fluid medium is aqueous.
 6. The polymer dispersionof claim 5, further comprising an active ingredient.
 7. The polymerdispersion of claim 6, wherein the active ingredient is a biocide. 8.The polymer dispersion of claim 1, wherein the plurality ofpoly(thioaminal) microparticles constitutes at least 50 wt % of thepolymer dispersion.
 9. The polymer dispersion of claim 1, wherein theplurality of poly(thioaminal) microparticles comprises polymer moleculeshaving S—C—N—R—N—C repeating units wherein R is an organic orhetero-organic group.
 10. The polymer dispersion of claim 1, wherein thefluid medium comprises a thiol-reactive material.
 11. A polymerdispersion, comprising: a plurality of poly(thioaminal) microparticles;a surfactant; and an aqueous fluid medium that does not dissolve theplurality of poly(thioaminal) microparticles.
 12. The polymer dispersionof claim 11, wherein the plurality of poly(thioaminal) microparticlescomprises polymer molecules having S—C—N—R—N—C repeating units wherein Ris an organic or hetero-organic group.
 13. The polymer dispersion ofclaim 12, further comprising an active ingredient.
 14. The polymerdispersion of claim 13, wherein the active ingredient is a biocide. 15.The polymer dispersion of claim 12, wherein the plurality ofpoly(thioaminal) microparticles constitutes at least 50 wt % of thepolymer dispersion.
 16. The polymer dispersion of claim 11, wherein theaqueous fluid medium comprises a thiol-reactive material.
 17. Thepolymer dispersion of claim 11, further comprising a pigment and abiocide, wherein the plurality of poly(thioaminal)-microparticlesconstitutes at least 50 wt % of the polymer dispersion, the aqueousfluid medium comprises water and a thiol-reactive material.
 18. Apolymer dispersion, comprising: a plurality of poly(thioaminal)microparticles; a surfactant; an active ingredient; a pigment; and anaqueous fluid medium comprising water and a thiol-reactive material thatdoes not dissolve the plurality of poly(thioaminal) microparticles. 19.The polymer dispersion of claim 18, further comprising an adhesive. 20.The polymer dispersion of claim 18, wherein the surfactant is an ionicsurfactant.